1. Field of the Invention
The present invention relates to an antifuse, and specifically to an over-etch of an antifuse via prior to the deposition of an antifuse layer, thereby ensuring a relatively tight programming voltage distribution irrespective of the underlying topology.
2. Description of the Related Art
Antifuses are well-known programmable elements in the integrated circuit industry. Antifuses have a high impedance state before programming, but change to a low impedance (i.e. permanently conductive) state after a programming voltage is applied across its electrodes. Antifuses are typically used in programmable logic devices to programmably interconnect conductive lines.
Various antifuse structures are described in detail in, for example: U.S. Pat. No. 4,881,114, issued Nov. 14, 1989 to Mohsen et al. (provides a dielectric between semiconductors of opposite conductivity type); U.S. Pat. No. 5,272,666, issued Dec. 21, 1993 to Tsang et al. (discloses methods of fabricating an antifuse having an area of less than one micron cell area); U.S. Pat. No. 5,319,238, issued Jun. 7, 1994 to Gorden et al. (teaches planar amorphous silicon antifuse structure); and an article titled "Antifuse Structure Comparison of Field Programmable Gate Arrays" by Chiang et al., IEDM IEEE, pp. 611-614 (1992)(compares various characteristics of multiple antifuse structures).
However, conventional antifuses are currently formed only on areas having no underlying structures, i.e. a flat topology. Specifically, as described in reference to FIGS. 1A-1F and 2A-2B, conventional antifuses formed on different topologies will produce different antifuse programming voltages. This variation in programming voltages highly undesirable. Thus, reduction in chip size is severely limited because active circuits cannot be placed underneath these conventional antifuse structures without undesirably increasing the programming voltage distribution. Therefore, a need exists for an antifuse which provides a narrow distribution of programming voltages irrespective of topology.